The present invention relates to a method and apparatus for an in situ analysis of ore concretions which lie on the sea floor and which are raised therefrom for performing the analysis.
The great demand for nickel and copper makes necessary the mining of even those deposits that are accessible only with difficulty, such as manganese lumps embedded in the sea floor at a depth of from 3,000 to 6,000 m. A decision whether these lumps are worth mining depends upon the precise knowledge of their content of usable metals. Large investments required for the necessary conveying equipment make mining appear profitable only where the fields have a size of several 10,000 km.sup.2. No method of analysis is known, however, which would permit verification of a sufficiently dense measuring grid on such sea floor surfaces with a justifiable expenditure of time.
In order to be able to make manganese lump analyses, for example, it is the practice to bring these manganese lumps from great depths (such as 6,000 m) and lift them on board ships by means of dredges. The time required to obtain a sample amounts to several hours, and further, the sample cannot be accurately associated with the sea floor coordinates. The lumps are then analyzed on board (and also in land-based laboratories) with wet chemical processes and by X-ray fluorescence methods, for which the samples must undergo extensive preparations.
Practically the only in situ analysis methods applicable are .gamma.-spectroscopic processes. Because of the special requirements for an analysis in water at pressures of several hundred bars with corresponding heavy reinforcements of the instruments, high transparence must be assured for the inducing (primary) and the induced (secondary) radiation. A comparison of the transmission of gamma radiation in 10 cm water for 20 keV, 1MeV, 10 MeV with the values 10.sup.-.sup.4 %, 50% and 80% in the same sequence shows that an X-ray fluorescence analysis must be excluded.